In recent years there has been considerable interest in the development of high-speed, high-power photoconductive switches for use in direct dc, or quasi-dc, to RF conversion thereof. The applications for this type of technology are primarily in the area of ultra-wide-band (UWB) radar, impulse radar, biological-effects testing, and high-speed diagnostic equipment. These applications require that the switching speeds be as fast as possible so that the generated electrical pulses contain the highest possible frequency components.
A recently introduced photoconductive switch, which is called the bistable (or bulk) optically controlled semiconductor switch (BOSS), (herein termed a BOSS switch) is disclosed in U.S. Pat. No. 4,825,061 ('061) of Schoenbach, et al, herein incorporated by reference. The operation of the BOSS switch disclosed in the '061 patent relies on persistent photoconductivity, which can be considered a gain mode, followed by photo-induced quenching to provide both BOSS switch closing and opening, respectively. A semi-insulating GaAs material is used in this BOSS switch and is manufactured by controlled electrical compensation of silicon-doped GaAs with copper (GaAs:Si:Cu). The process by which the GaAs:Si:Cu material may be manufactured is disclosed in U.S. Pat. No. 5,374,589 ('589) of Roush, et al teaching a thermally diffused copper process, herein incorporated by reference. We have determined that the BOSS switches formed of this copper-compensated, silicon-doped material (GaAs:Si:Cu) described in the '061 patent and manufactured by the thermal diffusing process of the '589 patent suffer a drawback in their inability to switch to their open or high resistance state in response to a subnanosecond light pulse having an operating wavelength in the 2-micron regime. This drawback limits the radio-frequency range for the applications of BOSS switches.
It is therefore an important object of the present invention to provide BOSS switches that may be switched into their open, high resistance state in response to a subnanosecond light pulse.